A rheology modifier (RM) can be used to increase the viscosity of a composition containing the RM. Conventional rheology modifying compositions that allow modification of viscosity of electrolyte-containing environments include cross-linked linear poly(vinyl amide/unsaturated carboxylic acid) copolymers, and cross-linked copolymers formed of unsaturated carboxylic acid, a hydrophobic mercaptan monomer, a thioester or amino acid containing chain transfer agent into the copolymer composition, and a cross-linking agent. For example, hydrophobically modified hydroxyethyl cellulose or ethylhydroxyethyl cellulose, hydrophobically modified ethoxylate urethanes, and hydrophobically modified alkali-soluble or swellable emulsions are known to modify rheology.